The present invention is related to copending U.S. patent application Nos. 07/460,459, now U.S. Pat. No. 5,040,187 and 07/607,341 still pending, which is a divisional of U.S. Pat. No. 07/460,459. The contents of these copending applications are incorporated herein by reference.
The present invention relates to a one-dimensional or two-dimensional laser diode array, and particularly to a structure for mounting one or a plurality of laser diodes on a substrate, which may or may not be monolithic, as a subassembly of a working laser device, and to a method of fabrication of such a subassembly. The invention has application in many areas in which high power semiconductor laser arrays are used, including satellite communications, directed energy applications, remote sensing of atmospheric conditions, range finding, and isotope separation. Other applications include optical recording, computing, laser machining, level sensing, and remote sensing.
The above-mentioned copending applications discuss known laser packaging techniques, and the deficiencies of those techniques. These applications describe and claim a less expensive, more efficient approach to manufacture of laser arrays through facilitation of mounting of laser diodes on a monolithic substrate.
FIG. 1A shows a monolithic substrate 10 provided according to the techniques described in the copending applications. The substrate 10 may be formed of BeO (which may be small grain BeO), AlN, or any highly thermally conductive material. The substrate 10 may be relatively large at first, and then may be cut into smaller arrays, or submounts, at an appropriate step in the fabrication process. Grooves 20 formed in the substrate 10 may be provided with a rounded bottom as shown.
Referring to FIG. 1B, metallization layer 30 is provided, using one or more of Cr, Ti, Ni, Au, or Ag, or alloys thereof, or any suitably conductive material that adheres sufficiently to the substrate. Metallization of the substrate decreases the size of the grooves. Metallization may be removed from the bottom of each groove by shadowing or masking to provide electrical isolation. As shown in FIG. 1C, after the metallization step, laser diodes 40 may be loaded into each array.
FIG. 2A shows a 2D array module with a solder bond 70, and a BeO heat spreader (which is optional) and electrical interconnect 75 with electrical isolation points 80. Heat flows from the array, through the heat spreader; light goes in the opposite direction. Instead of a heat spreader, a thicker substrate 10 may be used, in which case the thicker bottom portion of the substrate would spread heat. FIG. 2B shows the FIG. 2A structure, bonded via a solder bond 85 to a water-cooled copper heat sink 90. A polymide, fiberglass, or other suitable insulator 95 also is provided.
While the foregoing structure is advantageous because of the relative ease of fabrication of the array, it would be desirable to have a structure which did not require a separate metallization layer within the grooves into which the laser diodes are placed.